Problems on this page:
Machine stopping with nothing in the field
Hits OEE: Availability
Symptoms: The light curtain trips the machine when no one is near it.
Transmitter and receiver out of alignment
Realign the units using the alignment display, and check that the brackets cannot be knocked.
Lenses dirty with dust, oil mist or splashes
Clean the front windows with the cleaner the maker allows, on a set interval.
Vibration moving the brackets
Fit vibration-damping mounts and tighten the brackets.
Reflections from shiny surfaces nearby
Check the mounting against the maker distance from reflective surfaces.
Prevention: Nuisance trips recorded with the time, so a pattern can be seen.
Light curtain not stopping the machine
Hits OEE: Availability
Symptoms: A test piece passes through the field and the machine does not stop.
Muting or blanking set wider than allowed
Check the muting and blanking settings against the risk assessment; the machine must not run until it stops correctly.
Safety outputs bridged or bypassed
Remove any bypass and find why it was fitted.
Safety relay or controller fault
Have the safety circuit tested by qualified staff.
Wrong resolution for the hazard
Check the curtain resolution against the risk assessment.
Prevention: Test rod check at every shift start, recorded.
Machine stopping too late after a break
Hits OEE: Availability
Symptoms: The stopping time measured on the machine is longer than the safety distance allows.
Brake on the machine worn
Have the brake checked and the stopping time measured again.
Curtain mounted too close to the hazard
Check the mounting distance against the measured stopping time.
Response time settings changed
Check the curtain and safety controller settings.
Stopping time never measured after changes
Measure the stopping time after any change to the machine or its drives.
Prevention: Stopping time measured at the interval the site sets.
Muting not working
Hits OEE: Availability
Symptoms: Material passes and the curtain trips because muting did not start.
Muting sensors misaligned or dirty
Clean and align the muting sensors.
Muting timing outside the window
Check the timing between the muting sensors and the conveyor speed.
Pallet or load shape changed
Check the load against the muting sensor positions.
Muting lamp failed where one is required
Replace the muting lamp.
Prevention: Muting faults recorded per station.
Units damaged
Hits OEE: Availability
Symptoms: Curtain housings or windows are cracked or bent.
No protection from forklifts or loads
Fit protective guards or bollards around the units.
Windows scratched by cleaning
Use the soft cloth and cleaner the maker specifies.
Weld spatter or chips hitting the window
Fit protective shields made for the curtain.
Cable crushed
Route the cable in protection.
Prevention: Units inspected weekly.
Wrong unit fitted after replacement
Hits OEE: Availability
Symptoms: A replacement curtain does not work or is not configured.
Length or resolution different
Check the part number, length and resolution against the original.
Configuration not copied
Load the saved configuration and check muting and blanking settings.
Wiring code different
Check the connector pinout.
Not validated after fitting
Run the full validation test before releasing the machine.
Prevention: Validation record kept for every replacement.
Intermittent faults from wiring
Hits OEE: Availability
Symptoms: Light curtain faults come and go, often when the machine or a door moves.
Cable flexing at a moving part
Re-route the cable away from moving parts or use cable rated for flexing.
Connector loose or water inside
Tighten the connectors and check their seals.
Cable run beside power cables
Separate the curtain cable from drive and power cables.
Poor earth connection
Check the earth connection of the units and the controller.
Prevention: Fault codes recorded with the time and machine state.
Operators reaching around or over the curtain
Hits OEE: Availability
Symptoms: People reach the hazard without breaking the light field.
Gaps around the curtain not guarded
Fit fixed guards to close gaps at the sides, top and bottom.
Curtain height too low
Check the height against the risk assessment.
Someone can stand between curtain and hazard
Add a presence detection device or a horizontal curtain.
Guard removed for a job and not refitted
Check guards at every shift start.
Prevention: Guarding checked during safety walks.
Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.
Related equipment guides: PLC · photo-eye sensor · hydraulic press · industrial robot · proximity sensor
Stop the same fault coming back
Recurring safety light curtain stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.
Book a Fabrico demo
The directory stays free.
Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary
Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover